For the purposes of this patent, contact current is defined as the current that flows in an animal or human subject when the subject touches (contacts) two different electrically conductive points in the subject's environment. Different conductive points with different voltage potentials cause current to flow in the living body.
Most current measurement systems use one of two basic methods. The first method is to insert a known impedance into the current path and measure the voltage across the known impedance. (Current, voltage, and impedance are all related by Ohm's law, which states that Voltage=Current×Impedance. With two known quantities, one can calculate the unknown quantity, current in this case.) The second method is to attach a coupling transformer around the current path and measure the current via the magnetic field generated from the current flow.
Both methods have significant disadvantages for a contact meter; and at present there are no devices available to measure this contact current. The first method requires that the current path be broken with a fixed impedance and that the fixed impedance not significantly alter the measured current. For contact current, the points of contact can be anywhere on the body. The current flow will generally occur throughout the volume of the body. Contact points can occur at more than two locations with different voltages at each point. Consequently, it is difficult to gather and process this information.
The second measurement method (using a transformer) also has a number of disadvantages. Current transformers of this type are usually insensitive and must be used with large primary currents (Amps). Contact currents are typically small, milliamps (mA) and microamps (uA), and need a sensitive measurement device. Sensitivity can be increased by increasing the size and weight of the transformer, but this makes the devices too cumbersome for human use. Thus, prior art devices have not successfully measured contact current.
An additional problem is that the transformer method measures the magnetic field created by the current. Environments with potential contact currents often have ambient magnetic fields. The transformer measures both the magnetic field from the current flow and the ambient magnetic field, and cannot differentiate the two sources.
Accordingly, it is desirable to provide an improved technique for measuring current flow in an animal or human body.